Diagnostic Aids
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
- The hertz and millisecond parameters react immediately to any change in the FCS circuits, but may not react long enough to set this DTC.
- A reading of 16 Hz in the Freeze Frame/Failure Records indicates a circuit failure.
- An intermittent condition may not be detected because the sensor does not immediately power down and the connection may be restored before voltage drops below the operating threshold.
- If this DTC will not reset and the parameters are steady, thoroughly inspect all FCS circuits for an intermittent open.
- If a intermittent condition is suspected refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
DTC P0178
| Step | Action | Values | Yes | No |
|---|---|---|---|---|
| Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module (PCM) Connector End Views |
||||
| 1 | Did you perform the Diagnostic System Check-Engine Controls? | - | Go to Step 2 | Go to Diagnostic System Check - Engine Controls |
| 2 |
|
45 Hz | Go to Step 4 | Go to Step 3 |
| 3 |
|
- | Go to Step 4 | Go to Diagnostic Aids |
| 4 |
|
- | Go to Step 5 | Go to Step 9 |
| 5 | Connect a test lamp between the ignition 1 voltage circuit and the ground circuit of the FCS harness connector. Does the test lamp illuminate? |
- | Go to Step 6 | Go to Step 10 |
| 6 | Measure the voltage from the fuel temperature/composition signal circuit to a good ground with a DMM. Is the voltage within the specified range? |
4.3-5.2 V | Go to Step 7 | Go to Step 8 |
| 7 |
|
60 Hz | Go to Step 14 | Go to Step 11 |
| 8 | Test the fuel temperature/composition signal circuit for the following:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? |
- | Go to Step 16 | Go to Step 12 |
| 9 | Test the ignition 1 voltage circuit for an open or short to ground. Refer to Circuit Testing
in Wiring Systems. Did you find and correct the condition? |
- | Go to Step 16 | - |
| 10 | Test the ground circuit for an open. Refer to Circuit Testing
and Wiring Repairs
in Wiring Systems. Did you find and correct the condition? |
- | Go to Step 16 | - |
| 11 | Test the FCS signal circuit for an open or for high resistance. Refer to Circuit Testing
in Wiring Systems. Did you find and correct the condition? |
- | Go to Step 16 | Go to Step 12 |
| 12 | Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections
and Connector Repairs
in Wiring System. Did you find and correct the condition? |
- | Go to Step 16 | Go to Step 13 |
| 13 | Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement
. Did you complete the replacement? |
- | Go to Step 16 | - |
| 14 | Test for an intermittent and for a poor connection at the FCS. Refer to Testing for Intermittent Conditions and Poor Connections
and Connector Repairs
in Wiring Systems. Did you find and correct the condition? |
- | Go to Step 16 | Go to Step 15 |
| 15 | Replace the FCS. Refer to Fuel Composition Sensor Replacement (5.3L (L59) Engine)
. Did you complete the replacement? |
- | Go to Step 16 | - |
| 16 |
|
- | Go to Step 2 | Go to Step 17 |
| 17 | Observe the Capture Info with a scan tool. Are there any DTC's that have not been diagnosed? |
- | Go to Diagnostic Trouble Code (DTC) List | System OK |